Photoelectric speedometer, altimeter and course indicator



PHoToELEcTRIc SPEEDOMETER, ALTIMETER AND COURSE `INDICATOR Filed July14. 1959 l C. BOSCH July 5, 1960 7 Sheets-Sheet 1 Ihi w ev,

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PHOTOELECTRIC SPEEDOMETER, LTIMETER AND COURSE INDICATOR Filed July 14,1959 I 7 sheets-sheet 5 UN/ V/BRA 70)? C//QCU/T N0.

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PHOTOELECTRIC SPEEDOMETER, ALTMETER AND couRsE INDICATOR Filed July 14,1959 7 sheets-sheet 7 CELL No, l cf'LL N0. 2

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5AW TDTH GENER/I TOE OF .SCOPE Y AMpL/F/? 0F come Zo z z2 f3 t4 5INVENTOR ATTORNEYS nited States Patent PHOTOELECTRIC SPEEDOMETER,ALTIMETER AND COURSE INDICATOR I Carl Bosch, New York, N.Y., assignor toSperry Rand Corporation, Ford Instrument Company Division, Wilmington,Del., a corporation of Delaware Filed July 14, 1959, Ser. No. 827,052

6 claims. (cl. 25o- 209) This invention relates to navigation indicatingsystems and particularly to an electronic system which is adapted to beemployed in aircraft and like vehicles for indicating altitude, trueground speed and true course.

The navigation system which is arranged in accordance with thisinvention can be associated with simple mechanical or electricalcomputers so as to enable the pilot of a low fiying aircraft, forexample, to make aeronautical calculations without the use 'of radar,radio or other type of active transmission. Instead it employs thenatural radiation of light as the source of information. 'I his passivemanner of operation allows the pilot to maintain complete radio silence,thereby precluding jamming or detection as a consequence of itsoperation.

In general, the indicating system comprises a pair of photocells whichare vertically 4mounted one behind the other in the bottom of anaircraft either on a stable or rotatable platform and a third photocellin line with the first two photocells at an angle with the vertical. Theelectronic circuitry employs transistor switches which are controlled bya timer to connect normally two of the three cells into the system andto cause, for a given time duration, the other cell to be connected whenthe signal output of the first or second cell reach a preselected level.A pulse generator in the output is adapted to respond to either cell atthis level. If it is assumed that the radiation from the same object onthe ground causes the system to generate three consecutive pulsesinitiated by the respective cells, an indicator such as a cathode raytube having an appropriately calibrated face can beY l arranged todisplay the pulses as pips and values ofY ground speed and altitude, forexample, may be mentally derived therefrom. Also computers may beemployed to give the desired values directly.

There follows a more detailed description of a circuit arranged inaccordance with the inventive concept and illustrated in theaccompanying drawings, in which Fig. 1 is an illustration of the systemin an aircraft;

Fig. 2 is a block diagram illustrating a preferred circuit arrangement;A

Fig. 3 illustrates the geometric configuration of the aeronauticalproblem solved by the system;

Figs. 4, 4A, 4B and 4C are continuous schematic diagrams of the system;

Pig. 5 are time related wave diagrams for the principal components ofthe system.

Referring to the illustration of Fig. 1, lead photocell 1 and trailingphot'ocells 2 and 2a are the'radiation sensitive components which arespaced at a given vdistance apart from each other along the axis of theairborne vehicle being disposed toward the ground. As shown in the blackdiagram of Fig. 2, the cells 1 and 2 are connectable through transistorswitches 3 and 4, respectively, to amplifier 5 which applies one of theamplified signals from the photocells to a Schmitt trigger circuit 6.Also in the altitude section of the computer, which is arrangedidentically to the ground speed section, the cell 2 and the cell are'connectableto the amplifier 5a through transistor- '2,944,154 PatentedJuly s, 1960 switches 4a and 3a, respectively. The two sections beingidentical the ground speed section only will be specifically described.The trigger circuit 6 is adapted to deliver a positive square wave eachtime its input voltage exceeds a certain critical value and maintainthis square walve output asv long as the input voltage remains abovethis critical value. Difierentiator'7 is employed to differentiate theleading edge of the Schmitt trigger circuit outputpulse vand apply thisysharply rising and narrow pulseto univibrator 8 through transistor gate10. The univibrator is essentially a timer in control of the switchesbeing triggered by the differentiated pulse. The gate 10 holds theunifvibrator 8 inoperative while it is recovering. An output lead foreach state of the univibrator is in control of the switches 3 and 4 `thestate of which deter mine which` photocell output is to be applied tothe amplifier 5. The transistorized gate 10 is controlled by the squarewave output of univibrator 11 which is in turn triggered by one of theVstate output pulses of the univibrator 8. An oscilloscope 12 receivesthe output of the diierentiator 7 each time the4 Schmitt trigger circuit6 is fired. The Schmitt trigger circuit 6 is fired by the signalsgenerated vwhenever the lead cell and then the trailing cell which aregated in succession onto the amplifier 5 reach a preselected level. Thisis because the successive gating of .the cells onto the amplifierdetermines the time interval between observations and it is the timeinterval between observations of a ground object which causes the cellsto exceed a particular level and which is used to calculate velocity andaltitude either by mental operation` or by means of a simple computer.`

Obviously if velocity is desired the cells 1 and 2 in Fig. 1 would becells 1 and 2 in Fig. 3 so that tm can be determined as required in therelation for velocity, V, whereas, if altitude is desired, cells 2 and2a in Fig. 1 would be cells 2 and 2a in Fig. 3 so that time interval t32 may be ldetermined as required in the relation for altitude, H. Fig. 3illustrates the geometrical configuration of the system in an aircraft.Photocells 1 and 2 are mounted vertically at a distance a apart behindlenses of focal length F. Photocell 2a is tilted at an angle to thevertical and is placed so that its aperture is at a distance b from theaperture of cell 2. As the `landscape passes beneath the plane aparticular signal appears at the photocells in a time sequence such asto -appear first at cell 1, then at cell 2a, and finally at cell 2.Measurements made of these time intervals are then utilized in computingground speed and altitude as indicated in Equations (1) and (2),respectively. The derivation of Equation 2 is indicated in Fig. 3. Theface of the oscilloscope may have a calibrated scale so that the timebetween pip generations can be directly taken therefrom.

A detailed description of the system follows: l

Referring to Fig. 4 it may be seen that the multiplier cells 1 and 2 areconnected in the conventional manner to a negative 1000 volt regulatedpower supply 14. K ohm resistors 15 in the cell 1 and 100 K ohmresistors 16 .in the cell 2 are connected between each dynode therebysetting the dynodes at volt intervals and limiting the power supplycurrent to 1.0 milliampere per photocell. The anode of the cell 1 isconnected to a 51 K ohm amplifier input resistor 17 which is supplied bythey negativeV source 1,8 .and is K ohm resistor 20r andv the transistorswitch 3. The anode vof the cell 2 is connected to input resistor 21supplied by the'sourcejl, a grounded 2,0 K ohm resistor 22 and 4thetransistor switch 4." The amplifierl 5 comprising dual,v

triodes 2 3rand 24 is Ygrid connected to potentiometer 25 disposedbetween the resistors 17 and 21 and the sourceV rated condition. Thesaturated transistor thus effectively'V short circuits` its photocelland allows the signal of rthe Y'other cell to be applied to the inputofthe amplifier.

Control voltages for opening and saturating the transistor switches areobtained from-the univibrator circuit 8.

Zener `diodesf26 are used to direct couple the D.C. lamplifier v5 to theSchmitt circuit. A negative supply 29 and amplifier bias resistor 29avare connected into the coupling connection for the purpose of settingthe bias levely of the Schmitt circuit at some point below its controlvalue. The D.C. amplier 5 isprovided with a grid biasing potentiometer27 `supplied by the negative source 18 and grid biases the YSchmitttrigger circuitV 6 so that it eiectively establishes the'level of randomnoise signal which willy cause Vthe Schmitt trigger unit to tire.

' As shown in Fig. 4A the Schmitt trigger circuit 6 isa conventionalcathode coupled binary circuit having a capacitive coupling between theplate of triode'30 and the'grid of triode 31. The latter is normallylconducting also connected to grounded` 20 but is adapted to be cut offwhen an input signal appears on lthe grid of triode 30 and to yield tothe RC difierentiator 7 -a sharply increased-output which should attainrthe voltage level of the plate supply for the two tubes inv the triggercircuit. RC differentiator '7 is connected to receive this positiveoutput pulse of the trigger circuit on' conductor 32 in which there isdisposed a capacitor 33 and to which there are connected a groundedresistor 34 and a negatively poled diode 35.

The univibrator circuit 8 comprisesy a monostable multivibrator 3,6having a dual cathode follower 37 in! its out-y put. See Fig. 4B. Themonostable multivibrator 36 includes a pair of plate to grid coupledtriodes 38 and 49. Each of the triode coupling connections 41 and 424are capacitive and the connection 42 controlledby a potentiometer 43(see Fig. 4B) connecting iti to` the plate source. A plate resistor 444of the triode 46 is tapped by grid lead 45 which places' the'output ofthe` multivibrator' on the grid of triode 46 of the dual cathodefollower 3'7.

A grounded grid limiting lead 47 having a back to backA off the tube 59yas it begins toconduct due to the presence o f an incoming signal and toallow conduction through the tube 50 when it is in the offistate. A gridlimiting lead 56 having aback to `back diode V57' anda level .poten-Kt-iometer 5.58; is connected to the coupling grid leadSS.

Y The output of the univibrator circuit S is placed on the grid ot'.the; un-ivibratorV circuit 11 in Fig. 4C, which;

Vbecause* itis essentially' like the univibrator' circuit 8,

corresponding elements have been given the same reference charactersexcept for the letter a added thereto. Additionally, the coupii-ngcapacitor in the lead 42a is considerablyv smaller than the; coupling.Capacity in the lead 42; in orden to` reduce its time durationin theunstable state resulting'in a considerably smaller pulse width.

Cathode-follower tlisconventional in its arrangement,"

multivibrator is in the unstable condition. In operation the transistor3 is heldin the open condition byka positive voltage applied torits.base while the switch 4 is held in saturation by a negativev voltageapplied to itsl base. This permits the random' signalA from the cell 1to be applied to the amplifierY while-,the switch 4 is'efiectivelyshorting the signal fromxthecell 2.v Whena signal appears of suicientamplitude V'to re the Schmitt circuit, the univibrator 8 is triggeredcausing a negative voltage to appear at the baseY of the switch 3 and apositive voltage toappear at the base of the switch-4f.l This causestheswitch 3 to saturate or short vand the switch 4 to open thereby shortingthe cell I and allowing the signal of the cell 2 to be applied to theamplifier until the Vunivibrator circuit Sprelaxes toits normal state asdetermined by its time constant, at which time the initial conditionsprevail once more. Y

The amplifierv 5 is assumed to have a gain of 25. Four diodes 26 areused to direct couple the ampliiier output y voltage Vto theV Schmittcircuit 6. The potentiometer 27 in thegrid circuit is usedto adjust thelevel of random Vsignal which will cross the. critical levely and thusAcause As an example,

the Schmitt circuit to,l be triggered. assume the potentiometer isadjusted for a Zero signal f conditionof 149 volts yDC. at the plates ofthe amplifier 5f. As indicated in Fig. 4 the diodes will cause thisvoltage' to droplSS volts to 55 volts. 60 'volts D.C. is assumed to bethe critical level required for triggering the Schmitt circuit and hencea 5 volt signal would be sufri- SinceV the amplifier has va gain of V25,the required amplifier input voltage would be 5/25=0.2 volt. Therefore,for this particular potentiometer setting a random signal level of 20()millivolts would cause triggering of the Schmitt circuit. The ranv domsignal across the photocell load resistor 20 `is negative going and theoutput voltage across the amplier load resistor 29a is positive-going asrequired by the Schmitt f circuit. The negative 105 volt, D.C. supply29'is usedv to set the level of theSchmitt circuit at some point belowits critical value. v

Phot-ocell waveform of Fig. 5 illustrates a typical random pattern asobserved by the photocells. I Since at a time zo, univibrator circuit 8has not yet been triggered, switch 3 is in an o-pen circuit state whileswitch 4 is a short circuit. Therefore, the output of cell 1 is appliedto the amplier 5, and the amplier 5 will reproduce the random pattern ofcell. 1 up to time t1, as shown by the ampliier waveform. At timer t1the amplifier 5 output voltage crosses the critical level of the Schmitttrigger circuit 6, firing the Schmitt circuit, resulting in a positiveoutput pulse which is fed to the RC diiierentiator circuit 'l Yresultingin a sharply rising narrow positive pulse at the start ofthe squareIwave output voltage of the Schmitt circuit.-y The sharp negative pulseof the ditierentiatorisV short-circuited by the diode 35, resulting in asharp positive pulse which triggers univibrator circuit 8 and starts thesweep of the oscilloscope 12. However, at time t1;

' the triggering of theunivibrator'circuit 8 Vcauses transistor switch 3to be in a short circuit state and transistor switch 4 to be in opencircuit, thereby abruptly switching the. input of the amplier 5 to cell2. This switching action is accomplished by means of the positiverectangular output of the univibrat-or 8 being applied to the dual D.C.`cathode foilower 37. The back to back diodes 48 in Iits grid circuitsestablish the positive and negative extremes allow adjustment of theswitching pulses so as to prevent any coupling of these switching pulsesinto the amplier 5. Positive pulses cause the switches to open whilenegative pulses cause the switches to saturate. Since the photocellsignal is transmitted only during the time when its respective switch isopened, it is necessary for the pulses to be equal in magnitude and thusprevent any switching signal from entering the vamplier 5. If they arenot equal, the diiference Iwould be amplied by the amplifier 5, causingthe photocell signals to be lost in the switching signals. The levelpotentiometers 49 and 5S adjust the D.C. levels of each cathode follower46 and 50 so that the proper bias is applied to the base of'eachtransistor switch while the amplitude potentiometers 51 and 53 adjustthe positive swings of the switching signals. It is assumed that thelevel setting of +2.0 volts D.C. applied to the base of the transistorswitch 3 causes it to block while applying 5.0 volts D.C. to the base ofthe transistor switch 4 causes it to saturate.Y During the time intervalof the unstable state of the univibrator 8, the base of transistorswitch 3 drops to 4.0 volts D.C. causing it to saturate while that ofthe transistor switch 4 rises to +2.0 volts D.C. causing it to be in theblocked condition. Since the amplified output of cell 2 is now below thecritical level, the Schmitt circuit 6 will immediately return to itsnormal state. At time t2, the corresponding point on the random signalpattern as now seen by cell 2 crosses the critical level of the Schmittcircuit 6, -ring the Schmitt circuit again land causing a pip on theoscilloscope 12 display as illustrated on the Ioscilloscope waveform ofFig. 5. At time t3, univibrator circuit 8 returns to its normal state asdetermined by its time constant, switching the system backI to cell 1and triggering the univibrator circuit 11. Univibrator circuit 11 istriggered from the trailing edge of the output pulse of univibratorcircuit 8 and delivers a positive rectangular waveform to theconventional D.C. cathode follower 60 which in turn controls thetransistor gate causing the. gate 10 to be a short circuit for theduration of the univibrator circuit lll pulse, thereby preventing anysignal `from reaching univibrator circuit 8 during its recovery time.

The transistor gate 10 utilizes the NPN type being normally held in theblocked condition by a negative D.C. voltage applied to its base by thecathode follower 60. Upon arrival of a positive rectangular voltage fromthe cathode follower, the transistor switches into the saturatedcondition for the duration of the pulse. This shorts to ground theditferentiator output from the univibrator 8 and the oscilloscope 12 andrenders the system inoperative until the univibrator 36a returns to itsstable state causing the transistor gate to return to its blockedcondition.

Ground speed is obtained by measurement of the time interval between t1and t2 which may be a calibrated scale on the face of the oscilloscope.Altitude requires an additional time measurement from the cell 2ainclined at some angle to the vertical.

The photocells 1 and 2 may be supported by either a stable or arotatable platform on the airborne vehicle. The advantage of a rotatableplatform is that the system could be used to indicate true course. Thisis assured when the cells are rotated to a position where they arealigned with the ground track of the vehicle and the signal generated byeach cell is the same. The cells may be responsive to infrared radiationinstead of visual light as would be required for night time operation. v

Various modications may be made in the indicating d system withoutdeparting from the scope and principle of invention and dened in theappended claims.

What is claimed is:

l. An aeronautical value indicating circuit comprising a pair ofphotocells adapted to respond to ground radiation, a pulse generatoradapted to generate a pulse when its input signal reaches a given value,pulse responsive means connected to said generator and adapted to yieldan indication from which said values may be derived, a switchselectively connecting each of said photocells to said generator andtiming means connected to receive the output of said generator forcontrolling said switches, a gate disposed between said pulse generatorand said timing means and a second timing means and in control of saidgate, said gate -being arranged to isolate the iirst timing means andsaid pulse generator for a time duration determined by said secondtiming means.

2. An aeronautical value indicating circuit comprising a pair ofphotocells, a snorting-conducting switch connected to each photocell, apulse generator connected to said switches and adapted to generate apulse when its input signal reaches a given value, a pulse indicatorconnected to receive the output of said pulse generator, timing meansalso connected to receive the output of said pulse -generator and incontrol of each of said switches, a gate disposed between said pulsegenerator and said timing means and a second timing means connected toreceive the output of said first timing means and in control of saidgate, said gate being arranged to isolate the first timing means andsaid pulse generator for a time determined by said second timing means.

3. An aeronautical value indicating circuit comprising a pair ofphotocells, a shorting-conducting switch connected to each photocell, apulse generator connected to said switches and adapted to generate apulse when its input signal reaches a given Value, a pulse indicator'connected to receive the output of said pulse generator, timing meansalso connected to receive the output of said pulse generator and incontrol of each of said switches, a gate disposed between said pulsegenerator and said timing means and a second timing means connected toreceive the output of said first timing means and in control of saidgate, said gate being arranged to isolate the first timing means andsaid pulse generator for a time determined by said second timing means,said switching and rst timing means controlling said switches so thatone of the switches is normally conducting and the other of saidswitches is normally shorting the output of their connected photocellsand said rst timing means is arranged to cause the said one switch toshort and the said other switch to conduct the output of their connectedphotocells for a preselected duration of time.

4. An aeronautical value indicating circuit as claimed in claim 3wherein said timing'means are univibrators and said pulse generatorincludes an amplifier, a Schmitt trigger circuit and a diierentiator.

5. An aeronautical value indicating circuit as defined in claim 4wherein each of said univibrators includes a monostable multivibratorhaving a cathode follower in its output.

6. An aeronautical value indicating circuit as delined in claim 5wherein said gates and said switches include transistors the polarity ofwhose base electrodes are controlled by the univibrator of said firsttiming means.

References Cited in the file of this patent UNITED STATES PATENTS2,866,373 Doyle e: al. Dee. 3o, 195s

